Not sure what your bone to pick here, but no one's talking about airing down on washboard roads. @gaijin is simply quoting pressures...correctly...for IMPROVED roads (i.e. highways). We're not talking slower speeds and airing down. Hell I've run on the road for 10 miles between dirt running only 20 under my RAM. But I went slowly, didn't turn aggressively and got out of anyone's way that happened by.There are A LOT of factors why Toyota or any manufacturer to stipulate a higher tire pressure than required including fuel mileage, tire wear, handling, emergency handling.... lawsuits.... a lot of people are past GVWR. The TPMS doesn't not alert unless a certain threshold below recommended tire pressure. That's probably a factor too.
There's a range of pressure that is considered safe, none exceeding maximum pressure listed on the sidewall. All choices have compromises. There's optimal and there is acceptable. I'd even say the manufacturer's pressure listed on the TIP is less than optimal when loaded to GVWR. Should probably be 5-10psi higher than stated
There's already a buffer built in to the tire's load rating with a static load. The difference between dynamic load and static load is even greater when going off road in the sand or desert. Members here, including myself are running ~20psi for hundreds (some thousands) of miles over washboard and bumpy terrain without issue.... and with more weight. This is not the same as driving on the road but it is a testament to the strength of these LT tires. Running 37 psi on washboard roads would be more dangerous than 20 psi. Don't believe me? Try it.